This paper presents a historic account of the step function which has become the basis for calculating wind loads in stability analysis. The step function used in conjunction with accepted stability criteria provides a proven level of performance but it is discontinuous and cannot be directly modelled physically. For wind tunnel testing, a continuous power law formulation is required. This paper traces the origin and development of the step function. A power law with a reference height of 50feet and exponent of 0.1 was originally used to develop the profile; this was projected downward at 50-foot intervals causing discrete steps. This paper proposes a continuous power law formulation of the resulting step function with the commonly used 10m reference height. The exponent is based on a least-squares fit to the original height coefficients. The paper also examines the effect of different exponents on the wind over-turning moment and wind forces for a range of vessel types with different area versus height profiles. These are calculated using both a spreadsheet and available industry software. It was found that a power law of 10m-0.0883 provides the best fit to the final step function and is a continuous function that is recommended for wind tunnel testing for stability purposes.
A Boundary Layer Profile for Wind Tunnel Testing
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Breuer, John Andrew, Cheater, Brian, Chapman, Carl, Bhaumik, Tirtharaj, Masciola, Marco, Peak, Andrew, Wang, Tao, and James N. Brekke. "A Boundary Layer Profile for Wind Tunnel Testing." Paper presented at the SNAME 22nd Offshore Symposium, Houston, Texas, February 2017.
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